1. Field of the Invention
The present invention relates to an on-vehicle electronic control device and, more specifically, to an on-vehicle electronic control device incorporating a stabilized power supply circuit.
2. Background Art
In general, an on-vehicle electronic control device for fuel injection control, ignition control, air-supply valve switching control, etc. is comprised of a single piece of electronic circuit board enclosed built in a sealed box. And a control circuit comprised of input-output interface circuits in association with on-vehicle input-output equipment, microprocessor, and various memories are mounted on the mentioned electronic circuit board.
The mentioned interface circuits and control circuit are driven through a stabilized power supply circuit to which power is supplied by an on-vehicle battery, and a power supply circuit for such operation is mounted on the mentioned electronic circuit board.
In this respect, 1-chip type or 2-chip type microprocessors are popularly used and, further, some of 1-chip microprocessors are used in combination with a logical circuit portion. Therefore, in many cases, a plurality of main integrated circuits is employed in the mentioned electronic circuit board.
For example, in the Japanese Patent Publication (unexamined) No. 276267/2000 titled xe2x80x9cElectronic control device for vehiclesxe2x80x9d, first and second microprocessors are used and, further, constant voltage control power transistors and voltage control power supply integrated circuits (hereinafter xe2x80x9cintegrated circuitxe2x80x9d are hereinafter referred to as xe2x80x9cICxe2x80x9d) are incorporated.
Also, in the Japanese Patent Application No. 173124/2000 titled xe2x80x9cPower supply device for on-vehicle computing devicexe2x80x9d, an on-vehicle electronic control device is disclosed in which two systems of stabilized power supply, a 5V system and a 3.3V system, are provided by series transistors.
In the foregoing prior arts, in addition to the IC element working as an on-vehicle electronic control device, it is necessary to mount specific parts for constant voltage control circuit to obtain a stabilized power supply on the electronic circuit board or to add an IC element for power supply circuit.
Accordingly, a problem exists in that the constant voltage control circuit comprising specific parts increase occupancy area of the electronic circuit board, and particularly in the power supply of two systems, the occupancy area will become excessively large.
Further, even when specific parts or a dedicated IC element for voltage control are employed, if any imperfect contact or circuit disconnection takes place in voltage control feedback circuit, a switching element for feeding from power source may be fully conductive. As a result, there is a possibility of applying an excessive voltage to microprocessor, etc.
The present invention has been made to solve the above-discussed problems, and has an object of providing an on-vehicle electronic control device forming a power supply circuit not requiring any dedicated IC element or specific parts for voltage control and capable of improving safety level against trouble such as disconnection of voltage control feedback circuit, by incorporating a constant voltage control circuit in an on-vehicle electronic control IC element.
Another object of the invention is to provide an on-vehicle electronic control device forming a power supply circuit capable of improving inspection precision in current consumption of each individual IC element itself.
An on-vehicle electronic control device according to the invention includes: an IC element including an input-output interface circuit connected to on-vehicle input-output equipment and a control circuit; and in which a stabilized voltage is supplied from a power supply terminal connected to an on-vehicle battery to the IC element through a switching element.
The IC element incorporates a voltage control circuit for conduction control of the switching element so that a voltage of a first terminal to which an output voltage of the switching element is supplied becomes a predetermined voltage, and a second terminal to which an output voltage of the switching element is supplied.
And the input-output interface circuit and the control circuit are supplied with a power separately either from the first terminal or from the second terminal.
As a result, there is an advantage that number of parts is reduced and the on-vehicle electronic control device is small-sized as a whole, and assembly time can be shortened. Furthermore, inspection of current consumption can be performed with a high precision prior to incorporating the IC elements, and therefore defective rate of finished products is reduced.
It is preferable that the voltage control circuit includes: a comparison circuit for generating an output when a voltage of the first terminal, to which an output voltage of the switching element is supplied, is lower than a predetermined voltage; and a switching circuit for controlling conduction of the switching element depending on output of the comparison circuit.
As a result, constant voltage control for obtaining a stabilized voltage suitable for an on-vehicle electronic control device can be performed with a simplified circuit.
It is preferable that the on-vehicle electronic control device according to the invention further includes a second IC element including an input-output interface circuit, microprocessor and various memories; and a second switching element connected in series to the switching element for supplying a stabilized low voltage to the microprocessor and memories. And the input-output interface circuit for the microprocessor is supplied with a power from a third terminal connected to the output circuit of the switching element.
As a result, in the on-vehicle electronic control device having voltage control circuit of two systems, number of parts is reduced and the on-vehicle electronic control device is small-sized as a whole, and assembly time can be shortened. Furthermore, inspection of current consumption can be performed with a high precision prior to incorporating the IC elements, and therefore defective rate of finished products is reduced.
It is preferable that the voltage control circuit includes a second constant voltage control circuit comprising a second comparison circuit for generating an output when a voltage of a low voltage terminal, to which an output voltage of the second switching element is supplied, is lower than a predetermined voltage; and a second switching circuit for controlling conduction of the second switching element so that the stabilized low voltage is obtained depending on output of the second comparison circuit.
As a result, it is possible to perform a constant voltage control for obtaining stabilized voltage of two systems suitable for the on-vehicle electronic control device with a simple circuit.
It is preferable that a diode is incorporated and connected between the first and the second terminals of the IC element in such a manner that a direction from the second terminal to the first is a forward direction. And the comparison circuit is supplied with a power through the diode when any imperfect contact takes place in a circuit to which power is supplied from the first terminal.
As a result, it is possible to prevent the IC element from any trouble that may lead to a serious accident due to application of an excessive voltage to the IC element in case of a disconnection trouble in any feedback circuit for voltage control. Furthermore, inspection of current consumption can be performed with a high precision prior to incorporating the IC elements, and therefore defective rate of finished products is reduced.
It is preferable that the IC element incorporates an abnormal voltage comparison circuit for monitoring voltage variation in the second terminal and generating an alarm output when the monitored voltage exceeds a predetermined value.
As a result, when any imperfect contact occurs in the circuit, to which power is supplied from the first terminal, the alarm output is activated and gives a warning to stop the vehicle, urging the vehicle driver to repair the on-vehicle electronic control device.
It is preferable that the IC element includes a current detecting element for detecting a current running from the second terminal toward the first terminal, and an abnormal current comparison circuit for generating an alarm output when a current detected by the current detecting element exceeds a predetermined value.
It is preferable that the IC element includes a voltage comparison/memory circuit for monitoring voltage variation in the second terminal and acting on the switching circuit to shut off the switching element when the monitored voltage exceeds a predetermined value, and for storing such an abnormal state. And the voltage comparison/memory circuit is supplied with a power from an input voltage circuit of the switching element.
It is preferable that the IC element includes a current detecting element for detecting a current running from the second terminal toward the first terminal, and a current comparison/memory circuit for acting on the switching circuit to shut off the switching element when the monitored current exceeds a predetermined value, and stores such an abnormal state. And the current comparison/memory circuit is supplied with a power from an input voltage circuit of the switching element.
As a result, it is possible to prevent the interface circuit and control circuit of the IC element from any burning failure that may lead to a serious accident due to application of an excessive voltage to the IC element in case of a disconnection trouble in any circuit to which a power is supplied from the first terminal. Further, the switching element remains shut off, thus making it possible to promptly stop the vehicle.